Epidermal growth factor (EGF) and monoclonal antibody to cell surface EGF receptor bind to the same chromatin receptor

RETRACTED: The receptor tyrosine kinase AXL mediates nuclear translocation of the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a therapeutic target in patients with various cancers. Unfortunately, resistance to EGFR-targeted therapeutics is common. Previous studies identified two mechanisms of resistance to the EGFR monoclonal antibody cetuximab. Nuclear translocation of EGFR bypasses the inhibitory effects of cetuximab, and the receptor tyrosine kinase AXL mediates cetuximab resistance by maintaining EGFR activation and downstream signaling. Thus, we hypothesized that AXL mediated the nuclear translocation of EGFR in the setting of cetuximab resistance. Cetuximab-resistant clones of non-small cell lung cancer in culture and patient-derived xenografts in mice had increased abundance of AXL and nuclear EGFR (nEGFR). Cellular fractionation analysis, super-resolution microscopy, and electron microscopy revealed that genetic loss of AXL reduced the accumulation of nEGFR. SRC family kinases (SFKs) and HER family ligands promote the nuclear translocation of EGFR. We found that AXL knockdown reduced the expression of the genes encoding the SFK family members YES and LYN and the ligand neuregulin-1 (NRG1). AXL knockdown also decreased the interaction between EGFR and the related receptor HER3 and accumulation of HER3 in the nucleus. Overexpression of LYN and NRG1 in cells depleted of AXL resulted in accumulation of nEGFR, rescuing the deficit induced by lack of AXL. Collectively, these data uncover a previously unrecognized role for AXL in regulating the nuclear translocation of EGFR and suggest that AXL-mediated SFK and NRG1 expression promote this process.

Epidermal growth factor receptor targeted nuclear delivery and high-resolution whole cell X-ray imaging of Fe3O4@TiO2 nanoparticles in cancer cells

Sequestration within the cytoplasm often limits the efficacy of therapeutic nanoparticles that have specific subcellular targets. To allow for both cellular and subcellular nanoparticle delivery, we have created epidermal growth factor receptor (EGFR)-targeted Fe3O4@TiO2 nanoparticles that use the native intracellular trafficking of EGFR to improve internalization and nuclear translocation in EGFR-expressing HeLa cells. While bound to EGFR, these nanoparticles do not interfere with the interaction between EGFR and karyopherin-β, a protein that is critical for the translocation of ligand-bound EGFR to the nucleus. Thus, a portion of the EGFR-targeted nanoparticles taken up by the cells also reaches cell nuclei. We were able to track nanoparticle accumulation in cells by flow cytometry and nanoparticle subcellular distribution by confocal fluorescent microscopy indirectly, using fluorescently labeled nanoparticles. More importantly, we imaged and quantified intracellular nanoparticles directly, by their elemental signatures, using X-ray fluorescence microscopy at the Bionanoprobe, the first instrument of its kind in the world. The Bionanoprobe can focus hard X-rays down to a 30 nm spot size to map the positions of chemical elements tomographically within whole frozen-hydrated cells. Finally, we show that photoactivation of targeted nanoparticles in cell nuclei, dependent on successful EGFR nuclear accumulation, induces significantly more double-stranded DNA breaks than photoactivation of nanoparticles that remain exclusively in the cytoplasm.

Neurokinin 3 receptor forms a complex with acetylated histone H3 and H4 in hypothalamic neurons following hyperosmotic challenge

The neurokinin 3 receptor (NK3R) is a G protein-coupled receptor that is expressed in brain and is highly expressed by magnocellular vasopressinergic neurons in both the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus. Hyperosmolarity causes a ligand-mediated internalization of NK3Rs to the cytoplasm and to the nuclei of vasopressinergic PVN neurons. This receptor activation-dependent pathway is presumed to be a means to directly transmit synaptic signals from the cell membrane to the nucleus. The present study evaluated in vivo the subnuclear domains that associate with NK3R. Rats were administered 2 M NaCl (intragastric) or no intragastric load, and 40 min later, the PVN was dissected and nuclei were isolated. Using double-immuno-transmission electron microscopy (TEM), we show that, compared with controls, hyperosmolarity causes a significant increase in NK3R Immunogold beads in the nucleus of PVN neurons. Furthermore, NK3R spatially colocalized with histone H4 and with highly acetylated H4 in nuclei isolated from the PVN of rats administered 2 M NaCl, but not in nuclei from control rats. Next, coimmunoprecipitation experiments showed that acetylated H4, as well as acetylated H3, were pulled down with NK3R in the PVN nuclear enriched fraction from rats treated with 2 M NaCl, but not from control rats. In response to hyperosmolarity, NK3R is transported to the nucleus of PVN neurons and associates with transcriptionally active chromatin, where it may influence the transcription of genes.

In vitro toxicity of A-431 carcinoma cells with antibodies to epidermal growth factor receptor and epithelial glycoprotein-1 conjugated to radionuclides emitting low-energy electrons

PURPOSE

The ability of antibodies (Abs) conjugated to radionuclides emitting low-energy electrons to specifically kill nonadherent lymphoma target cells in vitro was demonstrated previously. This study extends this work to adherent carcinoma cells. The fact that these cells are spread out on plastic can potentially make it more difficult to deliver radiation to the nucleus from decays in the cytoplasm or on the cell surface.

EXPERIMENTAL DESIGN

The Abs tested were anti-epidermal growth factor receptor and anti-epithelial glycoprotein-1, conjugated to indium-111 or iodine-125, which emit low-energy Auger and conversion electrons. Conjugates of the beta-particle emitter, iodine-131, also were tested, for comparison. Abs were incubated with the cells for 2 days, and then the treated cells were assayed for colony-forming units. The radiation dose delivered to the nucleus was calculated from the cumulative decays per cell.

RESULTS

With conjugates of (111)In, very potent killing was obtained with both of the Abs, with 100% kill (approximately 4-5 logs) even at subsaturating Ab concentrations. Lower levels of kill were obtained with (125)I or (131)I conjugates. Conjugates with (131)I, a beta-particle emitter, produced greater nonspecific toxicity. The greater potency of (111)In could be attributed to the higher specific activity that was obtained routinely with this radiolabel, up to 70 mCi/mg. Uptake of radioactivity peaked at approximately 200 cpm per cell. Dosimetry calculations, using subcellular S values, demonstrated that the toxicity observed was consistent with the amount of radiation delivered to the nucleus.

CONCLUSIONS

These results are similar to previous results obtained with B lymphoma cells and indicate that this approach is applicable to a wide range of tumor types. Radionuclides emitting low-energy electrons are effective at killing target cells with relatively little nonspecific toxicity, if sufficient activity is delivered to the cell. Most Abs to high-density cell surface antigens would probably be effective.

Trafficking and signaling pathways of nuclear localizing protein ligands and their receptors

Interaction of ligands such as epidermal growth factor and interferon-gamma with the extracellular domains of their plasma membrane receptors results in internalization followed by translocation into the nucleus of the ligand and/or receptor. There has been reluctance, however, to ascribe signaling importance to this, the focus instead being on second messenger pathways, including mobilization of kinases and inducible transcription factors (TFs). The latter, however, fails to explain the fact that so many ligands stimulate the same second messenger cascades/TFs, and yet show distinct gene activation profiles. This is particularly apt in the case of the seven STAT TFs that are held to be the mediators of the distinct cellular functions of over 60 ligands. The current review focuses on five representative nuclear localizing ligands for which there is documentation of translocation into the cytosol and nucleus through well-characterized pathways, in addition to a role in gene activation by ligand/receptor in the nucleus.

Renal cell cultures for the study of growth factor interactions underlying kidney organogenesis

The present study was performed in four renal cell lines to evaluate their capability to: (1) produce and express transforming growth factor alpha (TGFalpha), its respective receptor, the epidermal growth factor receptor (EGFr) and the small G protein, RhoA, and (2) exhibit morphogenetic properties when grown on Matri-cell substrates. The cell lines were derived from normal (Madin-Darby canine kidney cells), embryonic (SK-NEP-1 and 293 cells), and cancerous (human renal adenocarcinoma cells) kidneys. TGFalpha messenger ribonucleic acid, evaluated by a nonradioactive in situ hybridization technique, was found to be expressed in all the cell lines. Large amounts of TGFalpha peptide were observed in all four cell lines, while EGFr was highly expressed only in cancerous ACHN and embryonic-tumor SK-NEP-1 cells. RhoA peptide was found in appreciable amounts in SK-NEP-1 and 293 cells (compared to the other two cell lines). The morphogenetic properties of the four cell lines were assessed, by culturing them on Matri-cell dishes: SK-NEP-1 cells alone were found to grow in three-dimensional structures forming clusters and worm-like cellular aggregates. This feature was displayed by SK-NEP-1 cells but not by the other three cell lines, and may be connected with the contemporary presence of RhoA, EGFr, and TGFalpha found in significant amounts only in the SK-NEP-1 cell line.

Demonstration of new sites of expression of the CCK-B/gastrin receptor in pancreatic acinar AR42J cells using immunoelectron microscopy

The CCK-B/gastrin receptor has been characterised in both normal and tumour tissues. Endocytosis of the CCK-B/gastrin receptor has recently been demonstrated and this has similarly been described for other peptide receptors. In addition, ligand and ligand-receptor translocation to the nucleus has been demonstrated for other peptides. The aim of this study was to identify the sites of expression of the CCK-B/gastrin receptor in the known CCK-B/gastrin receptor bearing pancreatic acinar AR42J cells. The specificity of the CCK-B/gastrin receptor antibody (alpha-CCKBR-Ser antibody) was demonstrated by inhibition ELISA studies, radioligand inhibition studies and immunofluorescence binding studies on AR42J cells. Western blotting and immunogold electron microscopy techniques were used to identify the receptor in AR42J cell preparations. The affinity purified alpha-CCKBR-Ser antibody was shown to be specific for the CCK-B/gastrin receptor. The receptor was expressed on the cell membrane, in the cytoplasm and within the nucleus. Isoforms of the receptor protein identified in extra-nuclear and nuclear extracts ranged in molecular weight from 58 to 66 kDa. We conclude that the CCK-B/gastrin receptor is not only expressed on the cell membrane, but also in the cytoplasm and nucleus of AR42J pancreatic acinar cells.

Cytoplasmic and nuclear cytokine receptor complexes

Much of our understanding on how hormones and cytokines transmit their message into the cell is based on the receptor activation at the plasma membrane. Many experimental in vitro models have established the paradigm for cytokine action based upon such activation of their cell surface receptor. The signaling from the plasma membrane activated cytokine receptor is driven to the nucleus by a rapid ricochet of protein phosphorylation, ultimately integrated as a differentiative, proliferative, or transcriptional message. The Janus kinase (JAK)--signal transducers and activators of transcription (STAT) pathway that was first thought to be cytokine receptor specific now appears to be activated by other noncytokine receptors. Also, evidence is accumulating showing that cytokines modulate the signal transduction machinery of the tyrosine kinase receptors and that of the heterotrimeric guanosine triphosphate (GTP)-binding protein-coupled receptors. Thus cytokine receptor signaling has become much more complex than originally hypothesized, challenging the established model of specificity of the action of a given cytokine. This review is focused on another level of complexity emerging within cytokine receptor superfamily signaling. Over the past 10 years, data from different laboratories have shown that cytokines and their receptors localize to intracellular compartments including the nucleus, and, in some cases, biological responses have been correlated with this unexpected location, raising the possibility that cytokines act as their own messenger through inter-actions with nuclear proteins. Thus, the interplay between cytokine receptor engagement and cellular signaling turns out to be more dynamic than originally suspected. The mechanisms and regulations of intracellular translocation of the cytokines, their receptors, and their signaling proteins are discussed in the context that such compartmentalization provides some of the specificity of the responses mediated by each cytokine.

A cell cycle regulating receptor is localized on cell surface and in nuclei of mitotically and meiotically dividing cells

We previously showed that a heterodimeric surface receptor of molecular weight 65,000 (p65) and 95,000 (p95) is expressed on the surface of proliferating cells such as activated T lymphocytes and neural precursors. This p65/p95 receptor is recognized by a monoclonal antibody and by type 3 reovirus hemagglutinin. Binding of the surface p65/p95 receptor leads to a growth arrest of mitotic cells and a consequent inhibition of proliferation. The p65/p95 receptor was demonstrated to be associated with kinase activity. Because p65/p95 is involved in the regulation of mitotic cell division, we sought to study the cellular distribution of the receptor and its possible role in meiotic cell division. Immunohistochemical labeling and flow cytometry studies were done using adult rat testes and cell lines. All cells undergoing mitotic or meiotic division in the rat testis expressed the p65/p95 receptor; cells that do not divide did not express receptors. Dividing cells had two receptor pools. As previously reported for several mitotically active tissues, a pool of receptors was localized on the cell surface. Interestingly, a pool of receptors was also seen intracellularly over the nucleus of labeled cells. The nuclear label seemed to be associated with chromosomes during specific stages of the mitotic and the two meiotic divisions, suggesting a role in the regulation of nuclear events. Further studies on this receptor and the function of the nuclear pool should provide a better understanding of the control of cell division.

Growth factor regulation of cell growth and proliferation in the nervous system. A new intracrine nuclear mechanism

This article discusses a novel intracrine mechanism of growth-factor action in the nervous system whereby fibroblast growth factor-2 (FGF-2) and its receptor accumulate in the cell nucleus and act as mediators in the control of cell growth and proliferation. In human and rat brain the levels and subcellular localization of FGF-2 differ between quiescent and reactive astrocytes. Quiescent cells express a low level of FGF-2, which is located predominantly within the cytoplasm. In reactive astrocytes, the expression of FGF-2 increases and the proteins are found in both the cytoplasm and nucleus. In glioma tumors, FGF-2 is overexpressed in the nuclei of neoplastic cells. Similar changes in FGF-2 expression and localization are found in vitro. The nuclear accumulation of FGF-2 reflects a transient activation of the FGF-2 gene by potentially novel transactivating factors interacting with an upstream regulatory promoter region. In parallel with FGF-2, the nuclei of astrocytes contain the high-affinity FGF-2 receptor, FGFR1. Nuclear FGFR1 is full length, retains kinase activity, and is localized within the nuclear interior in association with the nuclear matrix. Transfection of either FGF-2 or FGFR1 into cells that do not normally express these proteins results in their nuclear accumulation and concomitant increases in cell proliferation. A similar regulation of nuclear FGF-2 and FGFR1 is observed in neural crestderived adrenal medullary cells and of FGF-2 in the nuclei of cerebellar neurons. Thus, the regulation of the nuclear content of FGF-2 and FGFR1 could serve as a novel mechanism controlling growth and proliferation of glial and neuronal cells.

Nuclear accumulation of fibroblast growth factor receptors is regulated by multiple signals in adrenal medullary cells

In an effort to determine the localization of fibroblast growth factor (FGF) receptors (FGFR) that could mediate the intracellular action of FGF-2, we discovered the presence of high-affinity. FGF-2 binding sites in the nuclei of bovine adrenal medullary cells (BAMC). Western blot analysis demonstrated the presence of 103-, 118-, and 145-kDa forms of FGFR1 in nuclei isolated from BAMC. 125I-FGF-2 cross-linking to nuclear extracts followed by FGFR1 immunoprecipitation showed that FGFR1 can account for the nuclear FGF-2 binding sites. Nuclear FGFR1 has kinase activity and undergoes autophosphorylation. Immunocytochemistry with the use of confocal and electron microscopes demonstrated the presence of FGFR1 within the nuclear interior. Nuclear subfractionation followed by Western blot or immunoelectron microscopic analysis showed that the nuclear FGFR1 is contained in the nuclear matrix and the nucleoplasm. Agents that induce translocation of endogenous FGF-2 to the nucleus (forskolin, carbachol, or angiotensin II) increased the intranuclear accumulation of FGFR1. This accumulation was accompanied by an overall increase in FGF-2-inducible tyrosine kinase activity. Our findings suggest a novel mode for growth factor action whereby growth factor receptors translocate to the nucleus in parallel with their ligand and act as direct mediators of nuclear responses to cell stimulation.

Nuclear Translocation of fibroblast growth factor (FGF) receptors in response to FGF-2

Members of the FGF family of growth factors localize to the nuclei in a variety of different cell types. To determine whether FGF receptors are also present within nuclei and if this localization is regulated by FGFs, nuclei were prepared from quiescent and FGF-2-treated Swiss 3T3 fibroblasts and examined for the presence of FGF receptors by immunoblotting with an antibody produced against the extracellular domain of FGF receptor-1 (FGFR-1). Little or no FGFR-1 is detected in nuclei prepared from quiescent cells. When cells are treated with FGF-2, however, there is a time- and dose-dependent increase in the association of FGFR-1 immunoreactivity with the nucleus. In contrast, treatment with either EGF or 10% serum does not increase the association of FGFR-1 with the nucleus. When cell surface proteins are labeled with biotin, a biotinylated FGFR-1 is detected in the nuclear fraction prepared from FGF-2-treated, but not untreated, cells indicating that the nuclear-associated FGFR-1 immunoreactivity derives from the cell surface. The presence of FGFR-1 in the nuclei of FGF-2-treated cells was confirmed by immunostaining with a panel of different FGFR-1 antibodies, including one directed against the COOH-terminal domain of the protein. Fractionation of nuclei from FGF-2-treated cells indicates that nuclear FGFR-1 is localized to the nuclear matrix, suggesting that the receptor may play a role in regulating gene activity.

Inhibition of cancer cell growth by internalized immuno-histone conjugates

MAb NS 88 directed against breast cancer cells, which is internalized and translocated to the cell nucleus, was conjugated with histone and labeled with 125I. 125I-MAb-histone complexes (M(r) 250,000) were internalized by breast and cervical cancer cells and localized in the cytoplasm and chromatin. Electrophoretic analysis of the cells extracted from the conjugates revealed the same molecular weights of the cytoplasmic and chromatin complexes as those of the native conjugate. Nicotine (0.1%), which suppresses lysosomal degradation, stabilized the conjugates within the cell and prolonged the presence of nondegraded complexes inside the cytoplasm and chromatin from 1 day to at least 3 days. MAb-histone complexes, but not MAb alone, inhibited RNA synthesis and proliferation of cervical and breast cancer cells. A new application of internalized MAbs as the vehicles for protein inhibitors of transcription or replication is discussed.

Localization of Epidermal Growth Factor (EGF) and Epidermal Growth Factor Receptor (EGFr) in Human Pituitary Adenomas and Nontumorous Pituitaries: An Immunocytochemical Study

Epidermal growth factor (EGF) and epidermal growth factor receptor (EGFr) were investigated by immunocytochemistry (ICH) in 57 human pituitary adenomas and 10 nontumorous autopsy pituitaries. EGF immunoreactivity was demonstrated in 24 adenomas (42%), representing 23 functioning tumors and 1 nonfunctioning tumor of oncocytic type, and in all nontumorous pituitaries. Among 40 tumors, EGFr was found positive in 15 functioning adenomas (37.5%), representing 50% of them. The presence of both EGF and EGFr was found mainly in corticotroph adenomas (60%) and less frequently in somatotroph and lactotroph adenomas (20%). ICH on serial sections with EGF or EGFr and adrenocorticotrophic hormone (ACTH) or S-100 protein revealed that EGF and EGFr are localized specifically in corticotrophs and EGFr in stellate cells of nontumorous adenohypophysis. These results confirm the presence of EGF and EGFr in human pituitary adenomas and nontumorous pituitaries and highlight their frequent occurrence in hormone-producing adenomas. Further work is required to explore the possiblity that EGF and EGFr play a role in hormone production, release, and tumor progression.

Enhancement of monoclonal antibody efficacy: the effect of external beam radiation

External beam irradiation has been shown to enhance accumulation of monoclonal antibodies (MAb) in tumors in vivo. This effect is mainly attributed to an unspecific damage of vascular endothelial cells resulting in an increased vascular leakage. The aim of our studies was to determine the effects of external beam radiation on the expression and function of the epidermal growth factor receptor (EGF-R) in vivo. Expression and internalization of EGF-R was tested in vivo, employing 125I-MAb 425 that binds specifically to the human EGF-R. Irradiation of human high-grade glioma cell lines U87-MG and A1207 with increasing doses (0-3600 Rad) of 240 kVp X-rays, markedly enhanced the binding of 125I-MAb 425 to the cell surface. This effect could only be observed for a few days following irradiation. No correlation of the radiation dose and overexpression of EGF-R were found. At the same time, irradiation stimulated significant and dose-dependent internalization of 125I-MAb. Internalization and intranuclear accumulation of 125I-MAb are necessary to explain the radiocytotoxic effects of 125I. The combination of external beam irradiation and labeled MAb 425 showed at least additive effects on tumor cell survival, when the interval between irradiation and MAb treatment was short. Our data support the clinical observations in the adjuvant treatment of high grade gliomas with 125I-MAb 425 following surgery and external beam radiation.

Nuclear translocation of angiogenin in proliferating endothelial cells is essential to its angiogenic activity

The intracellular pathway of human angiogenin in calf pulmonary artery endothelial (CPAE) cells has been studied by immunofluorescence microscopy. Proliferating CPAE cells specifically endocytose native angiogenin and translocate it to the nucleus, where it accumulates in the nucleoli. Nuclear translocation of angiogenin does not occur in nonproliferative, confluent CPAE cells. These cells were previously found to express an angiogenin-binding protein (AngBP) that was identified as smooth muscle alpha-actin. Exogenous actin, an anti-actin antibody, heparin, and heparinase treatment all inhibit the internalization of angiogenin, suggesting the involvement of cell surface AngBP/actin and heparan sulfate proteoglycans in this process. It has been established that two regions of angiogenin are essential for its angiogenic activity, one is its endothelial cell binding site and the other its catalytic site capable of cleaving RNA. CPAE cells do not internalize four enzymatically active angiogenin derivatives whose cell binding site is modified, but they do internalize two enzymatically inactive mutants whose cell binding site is intact. Thus, the putative cell binding site of angiogenin is necessary for both endocytosis and nuclear translocation, but the catalytic site is not. Three other angiogenic molecules are also translocated to the nucleus of growing CPAE cells. Overall, the results suggest that nuclear translocation of angiogenin and other angiogenic molecules is a critical step in the process of angiogenesis.

Epidermal growth factor induced tyrosine phosphorylation of nuclear proteins associated with translocation of epidermal growth factor receptor into the nucleus

Treatment of human squamous carcinoma cells (HN5 cells) with epidermal growth factor (EGF) caused a time-dependent increase in tyrosine phosphorylation of six nuclear proteins of molecular mass 166, 140, 117, 95, 86 and 79 kDa. The major tyrosine phosphorylated protein was indistinguishable from the plasma membrane form of the epidermal growth factor receptor and was shown by enzyme linked immunosorbent assay (ELISA) to be translocated into the nucleus from extra-nuclear sites upon ligand stimulation. Using immunoelectron microscopy of both isolated nuclei and whole cells, epidermal growth factor receptor (EGF-R) was found to be associated with the chromatin and, to a lesser extent, with the inner surface of the nuclear membrane. Tyrosine phosphorylation of proteins other than EGF-R was particularly notable in the nucleoli. These observations suggest that EGF-R may exert some of its physiological functions by directly inducing tyrosine phosphorylation of specific nuclear proteins. Translocation of EGF-R to the nucleus may provide a vital link between plasma membrane signalling and gene activation.

Enhancement of epidermal growth factor receptor expression on glioma cells by recombinant tumor necrosis factor alpha

Recombinant tumor necrosis factor alpha (rTNF alpha; optimal dose 1000 U/ml) significantly increased the density of epidermal growth factor receptor (EGF-R) in three of four glioma cell lines in culture as determined by binding analysis of anti-EGF-R monoclonal antibody (mAb) 425. Since enhancement of EGF-R expression by rTNF-alpha was inhibited when cells were treated with the protein synthesis inhibitor cycloheximide, the effects of rTNF alpha may be protein-synthesis-dependent. The dose of rTNF alpha that was optimal for up-regulation of EGF-R on glioma cells did not inhibit the growth of these cells. 125I-labeled mAb 425 lysed glioma cells in culture following its internalization into the cells. After glioma cells had been treated with rTNF alpha, the growth-inhibitory effects of the mAb were significantly enhanced, probably a reflection of the increase in EGF-R density on the tumor cell surfaces. The rTNF alpha effects were specific to the EGF-R and did not affect unrelated glioma-associated antigens. In our previous clinical trials, 125I-labeled mAb 425 showed immunotherapeutic effects in glioma patients. The present study provides the basis for considerations of combined immunotherapy of glioma patients with 125I-labeled mAb 425 and rTNF alpha.

Epidermal growth factor and transforming growth factor alpha

I have attempted here to outline the basic biochemical knowledge that we have now secured on the EGF family of proteins. In the future we will learn much more about the differential role of EGF versus TGF-alpha, about the physiological significance of amphiregulin, the newest member of this family, and about the roles of TGF-alpha and amphiregulin in cancer. Many questions remain. What is the importance of these factors in embryogenesis and fetal development? Is there an involvement of the EGF-like domains of extracellular proteins in cell-to-extracellular-matrix interactions? Do these extracellular matrix EGF-like entities function in a similar manner to fibroblast growth factor in cell growth and in mediating the relationship of cells to the extracellular matrix? What is the significance of cell membrane-bound forms of EGF and TGF-alpha as potential cell-to-cell contact regulators? What is the role of the viral EGF-like proteins in the viral infective and transforming process? These and other questions will be addressed in the next decade. The key question has already been well stated: 'what is the normal physiological role of EGF during development and homeostasis? The answers to these and a host of other questions must be found before we can fully comprehend this important regulatory system' (Cohen, 1987).

Potentiation of DNA mediated gene transfer in NIH3T3 cells by activators of protein kinase C

The mechanisms involved in the translocation of exogenously added genetic information through the cellular cytoplasm and into the nucleus are essentially unknown. Several trans-cytoplasmic translocation systems operate within cells to transport information received by the plasma membrane into the nucleus. Protein kinase C may be functionally involved in many of these translocation mechanisms. In order to explore the involvement of protein kinase C activation in the cytoplasmic translocation of DNA, NIH3T3 fibroblasts were transfected using the calcium-phosphate co-precipitation method with a plasmid containing the lacZ gene and treated with tetradecanoylphorbol 12,13-acetate (TPA) or 1,2-dioctanoylglycerol (DiC8). Addition of TPA or DiC8 immediately after glycerol shock resulted in a 5-7-fold increase in the number of cells expressing beta-galactosidase as well as a concomitant increase in the total amount of beta-galactosidase activity in the population during periods of transient and stable expression. TPA added at later times resulted in lesser increases in the efficiency of transfection. In contrast, TPA added at the time of addition of the calcium-phosphate precipitate inhibited transfection. In support of a role for protein kinase C activation in enhancing DNA transfection, the TPA analog 4 alpha-phorbol 12,13-didecanoate, which does not activate protein kinase C, was ineffective at enhancing transfection. Furthermore, treatment of cells with the protein kinase C inhibitor sphingosine blocked the TPA-mediated increase in transient and stable expression. The results suggest that protein kinase C activation enhances transfection of exogenous DNA through an as yet unknown mechanism.

Chromatin and cell surface receptors mediate melanoma cell growth response to nerve growth factor

Growth response to nerve growth factor (NGF) was tested in the primary melanoma cell line WM 164, which expressed a low level of NGF cell-surface receptor, and in WM 164 cells transfected with cDNA for the cell-surface receptor (TrWM 164 cells), which expressed a higher level of the cell-surface receptor. Neither cell line expressed the chromatin receptor for NGF or internalized NGF. Both cell lines were stimulated to growth by NGF. After 10 d of exposure to NGF, a 230,000 Mr chromatin protein (receptor) was induced in both cell lines; as a result, NGF bound to the chromatin, and ribosomal RNA synthesis and cell proliferation were inhibited. We suggest that the cell-surface and chromatin receptors each mediate a different function of NGF.

Interaction of epidermal growth factor receptors with the cytoskeleton is related to receptor clustering

Recently it has been established that cytoskeleton-associated epidermal growth factor (EGF) receptors are predominantly of the high-affinity class and that EGF induces a recruitment of low-affinity receptors to the cytoskeleton. The nature of this EGF-induced receptor-cytoskeleton interaction, however, is still unknown. Therefore, we have studied the association of mutated EGF receptors with the cytoskeleton. Receptor deletion mutants lacking almost all intracellular amino acid residues displayed no interaction with the cytoskeleton, demonstrating that the cytoplasmic receptor domain is involved in this interaction. Further analysis revealed that receptor-cytoskeleton interaction is independent of receptor kinase activity and the C-terminal 126 amino acid residues, which include the auto-phosphorylation sites. Furthermore, it is shown that the high-affinity receptor subclass is not essential for association of low-affinity receptors to the cytoskeleton. EGF receptor-cytoskeleton interaction was increased, however, by treatment with sphingomyelinase, an enzyme known to induce membrane protein clustering, indicating that EGF receptor clustering may cause the association to the cytoskeleton.

Monoclonal antibody 425 inhibits growth stimulation of carcinoma cells by exogenous EGF and tumor-derived EGF/TGF-alpha

Carcinoma cells frequently coexpress transforming growth factor (TGF)-alpha and its receptor, the epidermal growth factor (EGF) receptor, implicating an autocrine function of carcinoma-derived TGF-alpha. Using a monoclonal antibody (425) to the EGF-receptor, we investigated the role of exogenous and tumor cell-derived EGF/TGF-alpha mitogenic activities in proliferation of cell lines derived from solid tumors. Monoclonal antibody 425 was chosen for these studies because it inhibits binding of EGF/TGF-alpha to the EGF-receptor and effectively blocks activation of the EGF-receptor by EGF/TGF-alpha. Seven malignant cell lines originating from carcinomas of colon, pancreas, breast, squamous epithelia, and bladder expressed surface EGF-receptor and secreted EGF/TGF-alpha-like mitogenic activities into their tissue culture media. All cell lines were maintained in a defined medium free of exogenous EGF/TGF-alpha. EGF and TGF-alpha added to the culture medium stimulated proliferation of five cell lines to comparable levels. EGF/TGF-alpha-dependent proliferation was significantly reduced by addition of MAb 425 to culture media. In addition, monoclonal antibody 425 reduced proliferation of the five EGF/TGF-alpha responsive cell lines in the absence of exogenous EGF/TGF-alpha. Antiproliferative effects induced by monoclonal antibody 425 were reversible and could be overcome by addition of EGF to culture media. Our results indicate that tumor-derived EGF-receptor-reactive mitogens can promote proliferation of carcinoma cells in an autocrine fashion.

Plasma membrane-mediated nuclear uptake and chromatin binding of insulin in tumor cell lines

Analysis of different cellular fractions after incubation of SW 948 and SW 707 colorectal carcinoma cells or WM 266-4 melanoma cells with 125I-insulin revealed the nondegraded hormone in the chromatin of these cells. Nuclear 125I-insulin was bound to specific fragments of EcoRI-, HaeIII-, and HincII-digested chromatin. A 45-kDa chromatin protein species that binds 125I-insulin was identified. Actinomycin D and cycloheximide inhibited the insulin-stimulated expression of chromatin receptors. Uptake of 125I-insulin by isolated nuclei occurred only in the presence of plasma membranes. Thus, at least some effects of insulin on target cells can be explained by direct gene regulation instead of "second messenger" action.

Antagonistic effect of PDGF and NGF on transcription of ribosomal DNA and tumor cell proliferation

The molecular mechanism by which NGF and PDGF affect growth of tumor cells was tested in human melanoma WM 266-4 and colorectal carcinoma SW 707 cell lines. We present evidence that NGF translocated to the nucleus and bound to the chromatin of SW 707 cells, which express the cell surface and the chromatin receptor for NGF, inhibits ribosomal RNA synthesis which in consequence leads to inhibition of cell proliferation. In WM 266-4 cells, which do not express NGF receptor, NGF does not affect cell proliferation. In contrast, PDGF translocated to the nucleus of both SW 707 and WM 266-4 cells activates ribosomal RNA synthesis. We report here that NGF abolishes PDGF-activated ribosomal RNA synthesis and PDGF-stimulated growth of tumor cells.

Nuclear uptake of monoclonal antibody to a surface glycoprotein and its effect on transcription

Nuclear transport and chromatin binding of monoclonal antibody (MAb) ME491, directed against a cell surface glycoprotein, was tested in intact cells and in a cell-free system. After a 24-h incubation with 125I-MAb ME491, the chromatin of melanoma cells and of colorectal carcinoma cells contained approximately 10 and 20%, respectively, of the antibody in nondegraded form. 125I-MAb ME491 was bound to a 55-kDa chromatin protein and localized in two HincII-digested chromatin fragments. Taken up by the nucleus, MAb ME491 inhibited transcription of ribosomal RNA genes by 70%. Nuclear uptake of 125I-MAb ME491 was increased up to ninefold when cells were preincubated with puromycin or actinomycin D. Nuclear uptake of MAb ME491 in a cell-free system was inhibited by ME491 antigen newly synthesized in the cytoplasm. Binding of 125I-MAb ME491 to the newly synthesized ME491 antigen caused precipitation of polysome-bound ME491 mRNA. The effect of MAb ME491 on transcription is discussed.

Intracellular receptor binding and nuclear transport of nerve growth factor in intact cells and a cell-free system

Nuclear uptake of 125I-labeled nerve growth factor (NGF) by cells that either express or do not express the cell surface receptor was tested using intact cells and a cell-free system. Intracellular and consequently nuclear uptake of NGF in intact cells was dependent on the presence of surface NGF receptor, whereas nuclear uptake in a cell-free system did not correlate with cell surface receptor expression. In the cell-free system, nuclear transport was inhibited when NGF receptor was being actively synthesized. Preincubation of intact cells with unlabeled NGF, cycloheximide, puromycin, or actinomycin D increased nuclear uptake up to threefold. The data suggest that, in intact cells, NGF transported into the cell via the surface receptors is also bound by the NGF receptor being synthesized in the cytoplasm. NGF taken up by the nucleus inhibited transcription of ribosomal RNA genes by 70% and, in turn, inhibited cell proliferation by 60%. A direct effect of NGF on transcription is discussed.